Hey CrossOps,
I haven't found the exact link I was telling you about yet (the different materials used, and light and longevity estimates), but it's in one of these links somewhere. also if you do a search with the for "greenhouse glazing" then narrow the search (using the search options) to .edu websites you should get a lot of good information on the subject.
Reference Sources
Related Links
Polythene greenhouse film facts - Clovis Lande
Resources for Greenhouse and Nursery Operations and Operators - Home - Virginia Cooperative Extension
Greenhouse Presentations
Horticultural Engineering - Rutgers University
GPNMag.com and Greenhouse Product News (GPN) magazine - Horticulture and Commercial Growers (a magazine dedicated to greenhouses)
Greenhouse Energy Resources
Here are some design plans for greenhouses I've ran across
http://www.pvcplans.com/ArchGrnHouse.pdf
free pvc greenhouse plans
FREE plans of PVC pipe structures, greenhouse, cold frame, furniture fittings
P.S.
That's probably what you already decided on, but I would put the greenhouse in the spot that gets the most sunlight through the day. If it ever becomes to much light, you can always use shade-cloth to cut down on the direct sun. But you cant move the greenhouse into the sun once it's built. Going by the list of plants you wish to grow, most if not all (except lettuce) are continuously fruiting plants, and continuously fruiting plants will do better with more light, rather than more shade.